Malawi's Vice-President Joyce Banda will take over the running of the southern African nation after the death of President Bingu wa Mutharika.

The government only officially confirmed the death of the 78-year-old earlier on Saturday, two days after Mutharika died following a heart attack.

The delay in the announcement had raised concerns about a political crisis because Banda had been expelled from Mutharika's ruling DPP party in 2010 after an argument about the succession, though she retained her state position.

Banda, 61, was due to be sworn in as president later on Saturday in the Chinese-built National Assembly in the capital Lilongwe, officials said. She will be southern Africa's first female head of state.

Banda appeared at a news conference earlier on Saturday to declare an official 10 days of mourning for Mutharika, who had ruled for eight years.

She ordered national flags to be flown at half-mast and the state broadcaster to play sombre music.

"I call upon all Malawians to remain calm and to keep the peace during this time of bereavement," said Banda, flanked by members of the cabinet, the attorney general and the heads of the army and the police.

Asked whether she was assuming the presidency, Banda, a women's rights activist, replied: "As you can see, the constitution prevails".

De facto successor

The Malawian constitution states the vice-president takes over if the president dies, but Mutharika appeared to have been grooming his brother Peter, the foreign minister, as his de facto successor.

Banda is expected to run the country until scheduled elections take place in 2014.

To convince the international community of the smooth transition, both the presidency and cabinet issued a statement assuring "that the constitution of the Republic of Malawi will be strictly adhered to in managing the transition".

Both Britain and the US which had been major donors to Malawi until they froze millions of dollars in aid over rows with Mutharika over his policies and actions, urged a smooth transition respecting the constitution.

William Hague, the UK foreign minister, said in a statement on Saturday: "I urge all sides to remain calm and [hope] that a peaceful handover takes place as provided for under Malawi's constitution."

There appeared to be little public sorrow at Mutharika's death.

Many of Malawi's 13 million people had viewed him as an autocrat personally responsible for an economic crisis that stemmed ultimately from a diplomatic row with former colonial power Britain a year ago.

Britain and others froze aid worth some 40 per cent of government spending, fuel supplies dried up and food prices soared, leading to popular unrest.

Medical sources said Mutharika's body was flown to South Africa because Malawi's energy crisis was so severe the Lilongwe state hospital would have been unable to conduct a proper autopsy or even keep his body refrigerated.